Analysis of Bayer Aluminate Liquors by thermometric titration

Significance of the Topic

The accurate determination of total caustic, total soda and aluminate in Bayer aluminate liquors is essential for process control, product quality and environmental compliance in the alumina industry. Rapid and reliable measurements help refineries optimize reagent consumption, avoid equipment corrosion and ensure consistent alumina yield.

Objectives and Study Overview

This study presents a thermometric titration procedure for sequential quantification of total hydroxyl (total caustic), carbonate (total soda) and aluminate content in Bayer process liquors. Based on established procedures by Watts & Utley and modified by Van Dalen & Ward, the method employs temperature‐driven endpoints to accelerate analysis and enable full automation.

Methodology and Instrumentation

The approach uses two complexation steps and two sequential titrations with standard hydrochloric acid. First, an aliquot of diluted liquor is treated with potassium sodium tartrate to liberate one hydroxyl per aluminate molecule, then titrated to determine total caustic (hydroxyl) and total soda (hydroxyl plus carbonate). Second, potassium fluoride is added to break the aluminotartrate complex, releasing three additional hydroxyl per aluminate, and a second thermometric titration yields the aluminate content. Calibration of titer and blank is performed by linear regression using TRIS standards and sample blanks.

Instrumentation Used

• Thermometric titrator with integrated temperature probe (Thermoprobe HF)
• Rod stirrer ensuring uniform mixing
• Precision buret (10 mL) for titrant delivery

Main Results and Discussion

Thermometric titration curves display distinct exothermic peaks for bicarbonate and hydroxyl endpoints. Endpoint detection is robust across a range of sample dilutions, with optimized stirring rates (10–15) and dosing rates (4 mL/min). Complexing solutions (potassium sodium tartrate ~614 g/L and KF ~620 g/L) remain stable above 22 °C. Regression‐based titer determination achieved high linearity (R²>0.999), and method blanks were reproducible, ensuring accurate correction for background heat effects.

Benefits and Practical Applications

• Rapid, fully automated sequence reduces operator time and error.
• High sensitivity and selectivity for hydroxyl and carbonate species.
• Adaptable aliquot sizes (up to 25 mL) accommodate a wide concentration range.
• Minimal sample preparation and direct use of standard reagents improve throughput.

Future Trends and Potential Applications

Integration with digital process control systems and Industry 4.0 platforms will enable real‐time monitoring and advanced process analytics. Further miniaturization of thermometric probes and development of enhanced data processing algorithms are expected to increase sensitivity and enable inline analysis. Expansion of the technique to other metallurgical and environmental matrices may broaden its applicability.

Conclusion

The thermometric titration method described delivers a fast, precise and automated solution for simultaneous determination of total caustic, total soda and aluminate in Bayer liquors. Its high reproducibility, clear thermal endpoints and low reagent requirements make it a valuable tool for quality assurance and process optimization in alumina production.

References

• Watts H. L., Utley D. W.: Sodium Gluconate as Complexing Agent in Volumetric Analysis of Aluminum Compounds, Anal. Chem. 28(11), 1731 (1956)
• Van Dalen E., Ward L. G.: Thermometric Titration Determination of Hydroxide and Alumina in Bayer Process Solutions, Anal. Chem. 45(13), 2248 (1973)
• Application Note H-131: Determination of Titer and Method Blank for Thermometric Titrations using tiamo
• Thermoprobe HF Leaflet, Metrohm, Doc. 8.109.8055